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Modern experimental techniques provide valuable information forunderstanding fatigue phenomena such as crack closure and crack paths in complexstress fields. Thermoelastic Stress Analysis is a non-contact technique that providesfull-field stress maps from the surface of structural components by measuring the smalltemperature changes at the surface of the structure arising from cyclic loading. Thetechnique appears to have great potential in the study of crack closure since the cracktip stresses are inferred from the temperature changes that occur in the component.This means that the effective stress intensity factor range of the growing crack can beevaluated directly from the experimental data. The preferred method of analysis toderive stress intensity factors is based on Muskhelishvili’s complex potentials. A newapproach has been developed that not only makes it possible to calculate the mode Iand mode II stress intensity factors but also to locate the crack tip and, consequently, tomonitor the fatigue crack path.In this paper is a description of the fundamentals of the thermoelastic stress analysistechnique and a summary of the different approaches to the experimental evaluation ofthe SIF. A description of the new methodology for the mathematical analysis ofthermoelastic images for the location of the crack tip is presented. The application ofthe latest TSA developments to two important structural integrity problems is presentedand discussed. The first is the evaluation of the effect of residual stresses on the closureof a fatigue crack growing through a weld. The second is the automatic tracking of afatigue crack growing from a starter defect. The advances made in dealing with boththese issues means that TSA likely to become an even more important tool in structuralintegrity research.